As a pulse width modulation (PWM modulation) method for a power conversion device using a main circuit constituted by six bridge-connected switching elements, it is conventional to us a “two-arm PWM modulation control”.
The two-arm PWM modulation control is a method in which the switching control on one phase among three phases is stopped for a certain time period and the switching controls on the other two phases are executed during this time period. With this method, because switching control on one of the phases is not executed, the switching loss can be reduced.
With the two-arm PWM modulation control, with the reduction effect of switching loss being considered, it is most effective to set the time period, during which switching control on one phase is stopped, to be near a peak value of a three-phase input/output current of a main circuit. A technique has been disclosed in which a phase voltage and a line current of any one of phases are detected; a power factor angle is thereby obtained; and on the basis of this power factor angle, PWM signals of respective phases are controlled such that a period during which switching is stopped follows near to the peak of a phase current (for example, Patent Literature 1).